In the provision of communication services within a wireless local area network (WLAN), the area is served by multiple interconnected wireless access points located throughout the area forming the network. Such a network may be installed in airports, shopping malls, office buildings, hospitals, and factories, as well as other locations where wireless accessibility may be desired. A wireless access point typically utilizes an omni-directional antenna that communicates with wireless devices, such as computers containing a network interface card (NICs) configured for WLAN communications. Telephones, paging devices, personal data assistants (PDAs), notebooks, and pocket notebooks, as well as other wireless devices, may also communicate using the network. The layout or configuration of the network, i.e., the spacing or separation of the wireless access points, may be determined by the data rate of communications between the network and the wireless devices, the modulation scheme used in those communications, and/or the propagation of communication signals from the wireless access points.
The Institute of Electrical and Electronics Engineers (IEEE) has promulgated three notable standards or communications protocols for WLANs. The first communications protocol, known as 802.11b, was based on proprietary or 2 Megabit per second (Mbps) products utilizing an unlicensed portion of the spectrum found at approximately 2.4 Gigahertz (GHz). The 802.11b communications protocol specifies a modulation scheme known as complementary code keying (CKK) to encode the wireless data in a format that fits within the bandwidth allotted under Federal Communications Commission (FCC) 802.11 direct-sequence spread-spectrum (DSSS) rules. CKK allows communications at data rates of up to 11 Mbps. Although the majority of WLANs in existence today are consistent with the 802.11b communications protocol, 802.11b WLANs are of limited utility since their speed is approximately that of a 10 Mbps Ethernet link.
Concurrent with the approval of the original 802.11b communications protocol, the IEEE approved the 802.11a communications protocol. The 802.11a communications protocol uses a modulation scheme referred to as orthogonal frequency division multiplexing (OFDM) to achieve a data rate of 54 Mbps through a portion of the spectrum located at approximately 5 GHz. A problem facing wireless network providers is that 802.11b and 802.11a WLANs were never intended to be compatible.
More recently, the 802.11g communications protocol has been promulgated, allowing data rates up to 54 Mbps within the 2.4 GHz band using OFDM.
Faced with the evolution of multiple communications protocols and a demand for increased data rates from subscribers, it may be desirable for a wireless network provider to upgrade an existing network, such as an 802.11b WLAN, to provide support for a newer communications protocol, such as 802.11a and/or 802.11g. Moreover, it may be desirable to support future communications protocols having increased data rates.
A concern in supporting more than one communications protocol is that the typical range of or propagation associated with a wireless access point configured for each of the existing communications protocols tends to be different. Such differences may be attributed to differing data rates, the modulation schemes, the number of channels, and/or the carrier frequencies used. in general, for example, the range of conventional 802.11b wireless access points is greater than that of those supporting the 802.11a or 802.11g protocols.
One approach to managing these differences is to reduce the data rate associated with that communications protocol that has the lesser range or propagation, as range tends to be inversely proportional to data rate. Such an approach thwarts the benefits of increased, or higher, data rates and is undesirable in the face of subscriber demands.
Another approach to managing these differences is to attenuate the radiation associated with that communications protocol that has the greater range or propagation. Such an approach may require more wireless access points, as wireless access points would need to be located closer together. Moreover, where an existing network is laid out based on a higher-range protocol, upgrading that network to a faster protocol may require a substantial re-layout of an existing WLAN, and a commensurate increase in costs. Time consuming additional planning may also be required, further increasing costs.
There is a need for a multi-band wireless access point for use in a wireless network capable of supporting multiple communications protocols with ranges that are effectively coextensive. Moreover, there is a need for a multi-band wireless access point capable of compensating for differences in propagation associated with one or more communications protocols.